#include <cstdio>
    #include <algorithm>
    #include <cstring>
    #include <iostream>
    using namespace std;
    #define INF 1e9
	int graph[1000][1000], m[1001], n;  //this is the array which I want to decrease
	int main(){
		int u, v, flag=0, testCase = 1;
    	while(scanf("%d%d", &u, &v), u||v){
 
        	n = 0;
            memset(m, 0, sizeof(m));
 
            for(int i = 0; i < 1000; i++)
            	for(int j=0; j<1000; j++)
                graph[i][j] = INF;
 
            if(!m[u])
            m[u] = ++n;
 
            if(!m[v])
            m[v] = ++n;
 
            graph[m[u]][m[v]] = 1;
            graph[m[u]][m[u]] = 0;
            graph[m[v]][m[v]] = 0;
 
    		while(scanf("%d%d", &u, &v), u||v){
            	if(!m[u])
            	m[u] = ++n;
 
        		if(!m[v])
            	m[v] = ++n;
 
            	graph[m[u]][m[v]] = 1;
            	graph[m[u]][m[u]] = 0;
            	graph[m[v]][m[v]] = 0;
        	}
 
            for(int k = 1; k <= n; k++)
            for(int i = 1; i <= n; i++)
            for(int j = 1; j <= n; j++)
                graph[i][j] = min(graph[i][j], graph[i][k] + graph[k][j]);
 
        	double s = 0.0;
 
            for(int i = 1; i <= n; i++)
            for(int j=1; j<=n; j++)
            s += graph[i][j];
            //cout<<s<<endl;
            s /= (double)n*(n-1);
            //cout<<s<<endl;
            printf("Case %d: average length between pages = %.3lf clicks\n",testCase++,s);
        }
        return 0;
        }

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